1. Field of the Invention
This invention relates to gas turbine engines and more specifically to centrifugal or axial/centrifugal engines having a pipe diffuser at the downstream end of the compression section.
2. Description of the Prior Art
Increasingly restrictive environmental pollution standards and dramatically increased fuel costs are causing engine manufacturers to devote substantial financial and personnel resources to the search for more efficient and cleaner combustion systems. Prior art techniques are no longer adequate and must be replaced in future engines with apparatus embodying technically superior systems.
Of the prior art systems known, U.S. Pat. Nos. 3,088,279 to Diedrich entitled "Radial Flow Gas Turbine Power Plant" and 3,238,718 to Hill entitled "Gas Turbine Engine" are considered to be illustrative of prior employed techniques. Both systems are suited to centrifugal or axial/centrifugal compression apparatus and employ radial inflow combustion technology.
In Diedrich a centrifugal impellor discharges medium gases radially into a diffuser. Radial vanes and axial vanes within the diffuser direct the medium gases to an annular chamber from which the gases are flowable into the combustor. High pressure, high velocity gases which discharge from the impellor during operation of the engine are partially decelerated within the diffuser and are further decelerated within the annular chamber after being dumped from the diffuser. Gases within the annular chamber remain at high pressure but have a substantially reduced velocity. Hill is a similar illustration of prior art techniques which diffuse the medium gases to a lower velocity. One feature of note in Hill is the pipes which carry the medium gases from the centrifugal impellor to the annular plenum chamber in which the combustors are disposed.
To the detriment of engine performance, a substantial portion of the velocity pressure head of the medium gases discharged from the compressors of the prior art engines is dissipated during the diffusion process.